Several types of plugging devices are known for sealing against an inner surface of a pipe, such as a well bore of an oil and/or gas well. The plugging device is lowered into the well in a retracted state or run state, and, at a desired location, the plugging device is actuated to expand radially from the retracted state to an expanded state or set state. Plugging devices typically comprises a slips device for anchoring of the plugging device to the inner surface of the well bore and a sealing device for sealing against the inner surface of the well bore, i.e. to separate the oil and gas below the sealing device from the area above the sealing device.
Typically, design parameters for plugging devices are the relationship between the outer diameter in the retracted state and the outer diameter in the expanded state, the temperature and pressure in the well etc.
One example of a prior art plugging device is shown in U.S. Pat. No. 7,178,602. Here, the difference between the outer diameter of the sealing device in the expanded state and the retracted state is relatively low, i.e. it is not possible to expand the sealing device much. In certain oil and gas wells, there is a need for plugging devices which must pass a relatively narrow part of a well bore and then be able to expand radially to seal a wider part of the well bore further down in the well. The above-mentioned plugging devices may not be used in many such well due to the limited expansion.
Another example of a prior art plugging device is disclosed in US 2004/0069502. Here, seal elements (30a, 30b, 30c) are provided partially outside each other in the run state, and by axial compression, the seal elements are pressed further outwards and hence are radially expanded to seal the well. In the set state, the seal elements form a cone-shaped seal body. Each seal element comprises several expansion fingers. The expanding seal elements are supported by an anti-extrusion system (40) which again are supported by backup rings (50) and also a cylindrical cone (60) connected to, and axially displaceable in relation to, the inner mandrel. The cone (60) is also acting as a pivoting point for the backup ring (50). It should be noted that each of the seal elements are in contact with the mandrel or are connected to connection devices in contact with the mandrel both in the run state and in the set state.
In certain wells, there is a desire to insert a plugging device through an insert safety valve, a straddle packer or other types of packers having a through fluid bore. In other wells, the well bore itself may have collapsed, allowing only small diameter plugging devices to pass.
Hence, the object of the present invention is to provide a plugging device capable of passing through a relatively narrow well bore while in its retracted state and thereafter be set and seal off a relatively wider well bore in the expanded state. Another object is to be able to use a wider range of materials in the sealing device.